The present invention concerns biocidal compositions. More especially, it concerns compositions comprising a silver compound supported on an oxidic support.
Many proposals have been made to utilise the antimicrobial action of silver and silver compounds since the Romans discovered the bactericidal or bacteriostatic properties of silver drinking vessels. We have previously described (EP 251 783 A) an antimicrobial composition comprising an antimicrobial silver compound deposited on an inert oxidic support The preferred composition is described as AgCl deposited on a support such as titania. The silver compound is deposited at a loading of 1-75% by weight of the support material, particularly at a loading of 15-25% by weight, that is, 0.99%-42.9% silver compound on the basis of the composite itself and assuming that the silver species is silver chloride. This antimicrobial material has been marketed and sold under the trade mark xe2x80x9cJMACxe2x80x9d.
JP 2-268103 (Kanebo and Tanaka) is a later disclosure of similar materials.
The said EP 251 783 teaches the use of the antimicrobial material as a component of a coating system, particularly for medical devices such as catheters, or for impregnating plastics objects. EP 251 783 teaches that the antimicrobial material is to be incorporated into a polymer in an amount of 5-60% by wt. Furthermore, it teaches the use of the composition to provide an antimicrobial effect into the environment encountered during use, and not primarily as protection of the device or composition into which it is incorporated from the environment itself, although the levels of material to provide the duty required will certainly protect the system from the environment.
We have now discovered that compositions comprising the JMAC product, show a surprising activity as biocidal and/or preservative components in a variety of materials, at concentrations very much lower than those previously recommended.
The present invention provides a composition protected against microorganism growth, especially against bacteria, yeasts and moulds, comprising a biocidal component which is a sparingly soluble silver compound deposited on a synthetic oxidic support at a loading of 1-75% by weight of the support, characterised in that said biocidal component is dispersed in said composition in an amount of from 5-1,000 ppm based on the total weight of the composition.
The actual concentration of the biocidal component depends upon the nature of the major component of the composition, and may be determined by routine testing. In some preferred embodiments of the present invention, concentrations are from 10-600 ppm, for example from 10-50 ppm of the biocidal component
The biocidal component is conveniently that marketed by Johnson Matthey PLC as xe2x80x9cJMACxe2x80x9d, but may be any similar material. Preferred silver compounds are silver chloride, although silver iodide, phosphate, hydroxide, carbonate, bromide, acetate, citrate, lactate, salicylate and stearate, as well as mixtures thereof with one another or with other silver compounds may be used. Preferred supports are titania and other stable oxidic supports comprising an oxide or hydroxide or comprising an oxy-anion species such as phosphate or sulphate. The biocidal component of the invention may be prepared in the same manner as described in the above-mentioned EP 251 783.
The solubilities of the silver compounds referred to above are shown below in Table I:
The above data was obtained from xe2x80x9cSolubilities of Organic and Inorganic Compoundsxe2x80x9d, Vol. 1, 4th Ed. By Stedel (Publisher: C. Van Nostrand).
The biocidal composition may usefully be surface modified, that is, surface coated or treated to provide desired physical and/or chemical properties to improve performance in the composition. For example, the biocidal component may be surface coated with a polymer such as PVA, PEG or PVP to provide a chemical and/or physical pathway for silver.
The composition of the invention may incorporate one or more diluents, adjuvants or other components, eg odour control substances, colouring or thickening substances and the like, that either have no substantial adverse effect on the biocidal properties of the silver containing component or have a beneficial effect. For example, other biocides may be incorporated, or a surfactant. It has been found that certain surfactants have a particularly and unexpectedly beneficial effect on the preservative properties of the biocidal component. An especially preferred surfactant is sodium dioctyl sulphosuccinate (hereinafter called xe2x80x9cDOSSxe2x80x9d), which may be purchased from a variety of sources. This substance is reported to have slight bactericidal properties and to enhance the activity of phenolic and mercurial disinfectants, but appears to show a remarkable synergy with the silver-containing biocidal component. One of the properties of DOSS is to act as a thickener, in general, we have found that most alternative thickeners, including the commonly used xanthate gums, tend to adversely affect the silver-containing biocidal component.
In a preferred embodiment, the biocidal component is suspended in a concentrate composition, eg containing 1-15 wt. % of biocidal component, together with about 15 wt. % of a DOSS solution, the balance being water. The DOSS solution may be in a glycol solvent, but other solvents, including alcohols, such as isopropyl alcohol or ethanol, may be used. For example, the DOSS may be present as a 60-70% by weight concentration in an alcohol/water or glycol/water mixture. Such a concentrate composition forms a part of the present invention. The concentrate composition is then available for dispersing into the final composition, at the desired concentration.
Another suitable concentrate composition according to the invention is an emulsion, either of the water-in-oil or the oil-in-water type, in which the biocidal component is dispersed in one of the phases. The emulsion can then, in turn, be dispersed into the desired material to be preserved. It may be appropriate, for some materials, for the emulsion to be broken at this stage.
The biocidal component is remarkably non-toxic for higher life forms, whilst being efficacious against a wide variety of micro-organisms, including bacteria, yeasts and moulds. This permits safe handling of the concentrate without excessive precautions, and demonstrates a remarkable contrast to prior existing preservatives in the art, which are all toxic organic compounds. The biocidal component remains effective at, on average, significantly lower concentrations in the final composition than most organic preservatives; the few organic preservatives that are effective at or around 5 ppm are extremely toxic in concentrated form.
The preserved compositions may be primarily a polymer or polymer solution or emulsion, for example a natural or synthetic latex, which may be intended for foaming to form a carpet backing, for coating or finishing fibres, fabrics or papers. The biocidal component may be incorporated into steam vulcanised latexes.
Other compositions of particular interest, and in which the biocidal component is effective, are cosmetics, both xe2x80x9cleave onxe2x80x9d and xe2x80x9crinse offxe2x80x9d type cosmetics, which can be subject to undesired bacterial growth, shampoos, sun-screens, water-based adhesives and paints, and detergent systems or liquid soaps. The composition may be, in a particular embodiment, a printing ink (whether or not pigmented) which may be printed or coated onto paper or plastics film packaging, for example to form a food packaging which inhibits microorganism growth at the interface between the packaging and a food product.
In another embodiment of the invention, the biocidal component is incorporated into a moulding, extruding or spinning plastics or polymeric composition, in sintered, foamed or blown compositions, in an amount of up to 0. 1% by wt; this is very much lower quantity than that taught in the EP 251 783 of 5 to 60 wt. %, exemplified by a 15-40 wt. % concentration for a 20% AgCl on TiO2 biocidal component.
To demonstrate the synergistic effect of the combination of commercial JMAC powder (20% silver chloride, 80% titanium dioxide) and DOSS, tests were carried out to compare the Minimum Inhibitory Concentration (MIC) of the powder as a dry solid (product 1), a combination of JMAC and DOSS (10% JMAC powder, 9% DOSS, 2.25% alcohol and 78.75% waterxe2x80x94product 2), a concentrate composition according to the invention, and a commercial DOSS solution (70% DOSS, 15% water and 15% polyethylene glycolxe2x80x94product 3), for a wide variety of microorganisms.
The results are shown below in the Table, from which it can readily be seen that although the JMAC powder (product 1) shows the lowest MIC, ie is the most potent, and the DOSS solution (product 3) has relatively little potency, the JMAC+DOSS mixture (product 2) is surprisingly effective given that the concentration of JMAC powder is only 10% of product 1. That is, the actual concentration of biocidal silver is much reduced in product 2 and a MIC of 400 becomes the equivalent to 40 ppm of JMAC powder (product 1). This 10-fold equivalent reduction is shown in the brackets for product 2 in the Table.